The present invention relates to a prismatic wood compression molding method, more precisely relates to a prismatic wood compression molding method, in which prismatic wood having a polygonal sectional shape, e.g., rectangular, hexagonal, is formed by compressing wood, the compressed state of the wood is maintained and the compressed wood is heat-treated so as to permanently fix the prismatic shape of the compressed wood.
Conventionally, compressed lumber is manufactured by the steps of: compressing wood, e.g., needle-leaf wood; accommodating the compressed wood in a container; and heating the compressed wood by introducing steam into the container so as to permanently fix the shape of the compressed wood whose hardness is almost equal to that of broadleaf wood.
To heat-treat the wood in the container by steam, the container must be a pressure container, it is difficult to simultaneously treat a large amount of wood in a large container, and manufacturing efficiency must be lower.
Japanese Patent Gazette No. 7-47511 disclosed a method of permanently fixing a shape of compressed wood, the method comprises the steps of: compressing raw wood, whose water content is about 20 %, by a compressing die set; air-tightly accommodating the compressed wood in a container, in which a clearance is formed between the compressed wood and an inner face thereof; and heating the compressed wood in the container.
In the method disclosed in the Japanese patent gazette, the compressed wood is wet-heated by using water included in the wood, so that the compressed shape can be fixed in a short time. In comparison with the method in which the wood in the pressure container is heated by introducing steam thereunto, the wood can be compressed and the compressed shape thereof can be permanently fixed by a simple facility.
However, in the method disclosed in the Japanese patent gazette, the wood is compressed by the compressing die set, then the compressed wood is heat-treated in the die set.
If the wood to be compressed is longer than the compressing die set, it is difficult to compress the wood throughout length thereof, therefore size of the die set for compressing long wood must be large. So size of the wood depends on the size of the compressing die set.
In the case of heating the raw wood whose water content is about 20%, vapor is emitted while heating; the compressing die set must be made of stainless steel, so that the compressing die set must be expensive and manufacturing cost of the compressed lumber must high.
Generally, length of prismatic pillars for wooden building are several meters, so it is very difficult to compress long wood by the method disclosed in the Japanese patent gazette due to size of the compressing die set and the manufacturing cost.
A fist object of the present invention is to provide a prismatic wood compression molding method capable of easily manufacturing compressed prismatic wood for pillars, etc.
A second object of the present invention is to provide a compression molding device for executing said method.
The inventors of the present invention have studied and found that rectangular wood can be formed by compressing wood with four rigid metal plates whose length is equal to that of the wood and that the metal plates can compress the wood throughout the length thereof by pressing center portions of the metal plates by an upper die and a lower die of a compressing die set.
Further, the inventors found that a band-shaped member clamping the four metal plates, which compress flat outer faces of the compressed wood, is capable of maintaining the compressed state of the wood after the compressing die set releases the compressed wood, and that the compressed shape of the wood can be permanently fixed by applying a heat treatment to the prismatic wood which has been compressed by the four metal plates and the band-shaped member.
To achieve the first object of the present invention, the prismatic wood compression molding method comprises the steps of: compressing an outer circumferential face of wood throughout of length of the wood by a plurality of rigid plate-like bodies such as metal plates to form into prismatic wood which is polygonal, such as rectangular or hexagonal, in cross section; restraining the plate-like bodies by a restrain jig so as to hold flat surfaces of the prismatic wood in a state in which they are compressed by the plate-like bodies; and applying a heat treatment to the prismatic wood held in the compressed state by the plate-like bodies and the jig so as to permanently fix the shape of the prismatic wood.
To achieve the second object of the present invention, the compression molding device for manufacturing compressed prismatic lumber comprises: a compression molding die set including an upper die and a lower die, which form a cavity, which is polygonal such as rectangular or hexagonal, when they are closed; a plurality of plate-like bodies, such as metal plates, compressing an outer circumferential face of wood throughout of length thereof so as to form into prismatic wood which is polygonal, such as rectangular or hexagonal, in cross section; and a restraint jig restraining the plate-like bodies so as to hold flat surfaces of the prismatic wood in a state in which they are compressed.
Further, the second object of the present invention can be achieved by the compression molding device for manufacturing compressed prismatic lumber comprising: a compression molding die set for compressing an outer circumferential face of wood so as to form into prismatic wood which is polygonal, such as rectangular or hexagonal, in cross section; and a cylindrical die having transverse sectional shape, which is polygonal such as rectangular or hexagonal, corresponding to that of the prismatic wood, wherein an outlet of the compression molding die set and an inlet of the cylindrical die are arranged close so as to insert the compressed wood into the cylindrical die.
In the present invention, a plurality of the rigid plate-like bodies such as metal plates respectively compress the outer flat faces of the compressed wood, the restraining jig restrains the plate-like bodies to maintain the compressed state, then the compressed prismatic wood is heat-treated.
Therefore, the compressed wood can be taken out from the compressing die set and heat-treated, so the compressing die set need not be installed in heat-treating atmosphere. So the compressing die set can be made of steel, which is more inexpensive than stainless steel.
Since the wood is directly compressed by the plate-like bodies, length of the plate-like bodies can be selected on the basis of length of the wood. Even if the wood is longer than the compressing die set, the plate-like bodies which contact the wood throughout length thereof are partially pressed by the inner faces of the cavity of the dies of the compressing die set, so that long compressed lumber having a prismatic sectional shape can be manufactured.
Further, the compressed state can be maintained by inserting the compressed prismatic wood in the cylindrical die whose sectional shape is polygonal shape. By applying the heat treatment to the compressed prismatic wood, the prismatic shape of the wood can be permanently fixed. Namely, long compressed prismatic wood can be easily manufactured by the long prismatic cylindrical die.